Typically, refrigeration systems utilize a compressor to compress a refrigerant gas, a condenser to cool the compressed gas and to cause the gas to condense to a liquid and an evaporator for absorbing heat from the area to be refrigerated as the liquid refrigerant expands and evaporates. In many such systems, oil is used as a lubricant and to provide a more effective seal in the compressor. By such use, oil is mixed with the refrigerant gas in the compressor, and is carried along with the refrigerant. Oil, however, is not a refrigerant; it reduces the efficiency of the system if the oil is permitted to remain mixed with the refrigerant gas as it moves to the condenser. Therefore, it is known to provide an oil separator in the line between the compressor and condenser to remove the oil from the refrigerant gas. Generally, refrigerant gas from the compressor contains oil in the form of a fog as it enters the oil separator inlet.
Various arrangements have been provided for separating the oil from the gas. For example, U.S. Pat. No. 3,778,984 discloses an arrangement for introducing the oil and gas mixture tangentially to a separator so as to centrifuge the oil from the gas so that the oil will fall downwardly under the force of gravity into a collecting chamber in the bottom of the separator. U.S. Pat. No. 4,478,050 discloses an oil separator in which fluid is introduced tangentially in a chamber bounded by a screen upon which the oil particles collect. The oil and refrigerant mixture is caused to flow in a vortex providing centrifugal separation of oil particles. Deflector tabs are provided to enhance or regenerate the vortex in the lower portion of the chamber above oil outlet opening. U.S. Pat. No. 4,263,029 discloses an oil separator in which fluid is introduced tangentially in a passageway formed by a spiral wall having a single revolution. The fluid then passes to a chamber bounded by an annular ring and then to a chamber bounded by a funnel shaped wall with a central opening for passage therethrough of collected oil and including vanes for guiding the oil to the opening. The "oil free" gas leaves the separator through a central, axial passage.
U.S. Pat. No. 5,113,671 discloses an oil separator in which the oil/refrigerant mixture is caused to flow in a generally spiral flow path along the peripheral wall of the oil separator chamber so as to increase the effective path length of the oil/refrigerant mixture along the peripheral wall. A screen mesh is provided along the wall to enhance the separation of oil from the mixture and to provide a collection area for the separated oil. The separated oil drips from the screen to an inverted funnel/baffle which has a plurality of drain holes therethrough to allow the separated oil to drop into an oil collection chamber. A float valve arrangement is provided in the oil collection chamber which permits periodic dispensing of the oil from the chamber to an oil reservoir.
Although some known oil separators provide more than one mode of filtration, they do so in a single filtration chamber. Consequently, such filters cannot filter out oil vapor in increasingly fine, discrete filtration modes. Furthermore, in separators having more than one filter element, it is impossible or difficult at best, to gain access to filter elements for maintenance or replacement.